Ubuntu Manpage: xfsctl - control XFS filesystems and individual files

Provided by: xfslibs-dev_5.3.0-1ubuntu2.1_amd64

NAME

       xfsctl - control XFS filesystems and individual files

C SYNOPSIS

       #include <xfs/xfs.h>

       int xfsctl(const char *path, int fd, int cmd, void *ptr);

       int platform_test_xfs_fd(int fd);
       int platform_test_xfs_path(const char *path);

DESCRIPTION

Some functionality specific to the XFS filesystem is accessible to applications through platform-specific
system call interfaces. These operations can be divided into two sections - operations that operate on
individual files, and operations that operate on the filesystem itself. Care should be taken when issuing
xfsctl() calls to ensure the target path and file descriptor (both must be supplied) do indeed represent
a file from an XFS filesystem. The statfs(2) and fstatfs(2) system calls can be used to determine
whether or not an arbitrary path or file descriptor belong to an XFS filesystem. These are not portable
however, so the routines platform_test_xfs_fd() and platform_test_xfs_path() provide a platform-
independent mechanism.

File Operations
In order to effect an operation on an individual file, the pathname and descriptor arguments passed to
xfsctl identifies the file being operated on. The final argument described below refers to the final
argument of xfsctl. All of the data structures and macros mentioned below are defined in the
<xfs/xfs_fs.h> header file.

XFS_IOC_ALLOCSP
XFS_IOC_ALLOCSP64
XFS_IOC_FREESP
XFS_IOC_FREESP64
Alter storage space associated with a section of the ordinary file specified. The section is
specified by a variable of type xfs_flock64_t, pointed to by the final argument. The data type
xfs_flock64_t contains the following members: l_whence is 0, 1, or 2 to indicate that the relative
offset l_start will be measured from the start of the file, the current position, or the end of
the file, respectively (i.e., l_start is the offset from the position specified in l_whence). If
the offset specified is before the current end of file, any data previously written into this
section is no longer accessible. If the offset specified is beyond the current end of file, the
file is grown and filled with zeroes. The l_len field is currently ignored, and should be set to
zero.

XFS_IOC_ALLOCSP, XFS_IOC_ALLOCSP64, XFS_IOC_FREESP and XFS_IOC_FREESP64 operations are all
identical.

XFS_IOC_FSSETDM
Set the di_dmevmask and di_dmstate fields in an XFS on-disk inode. The only legitimate values for
these fields are those previously returned in the bs_dmevmask and bs_dmstate fields of the
bulkstat structure. The data referred to by the final argument is a struct fsdmidata. This
structure's members are fsd_dmevmask and fsd_dmstate. The di_dmevmask field is set to the value
in fsd_dmevmask. The di_dmstate field is set to the value in fsd_dmstate. This command is
restricted to root or to processes with device management capabilities. Its sole purpose is to
allow backup and restore programs to restore the aforementioned critical on-disk inode fields.

XFS_IOC_DIOINFO
Get information required to perform direct I/O on the specified file descriptor. Direct I/O is
performed directly to and from a user's data buffer. Since the kernel's buffer cache is no longer
between the two, the user's data buffer must conform to the same type of constraints as required
for accessing a raw disk partition. The final argument points to a variable of type struct
dioattr, which contains the following members: d_mem is the memory alignment requirement of the
user's data buffer. d_miniosz specifies block size, minimum I/O request size, and I/O alignment.
The size of all I/O requests must be a multiple of this amount and the value of the seek pointer
at the time of the I/O request must also be an integer multiple of this amount. d_maxiosz is the
maximum I/O request size which can be performed on the file descriptor. If an I/O request does
not meet these constraints, the read(2) or write(2) will fail with EINVAL. All I/O requests are
kept consistent with any data brought into the cache with an access through a non-direct I/O file
descriptor.

XFS_IOC_FSGETXATTR
XFS_IOC_FSGETXATTRA
XFS_IOC_FSSETXATTR
See ioctl_xfs_fsgetxattr(2) for more information.

XFS_IOC_GETBMAP
XFS_IOC_GETBMAPA
XFS_IOC_GETBMAPX
See ioctl_getbmap(2) for more information.

XFS_IOC_RESVSP
XFS_IOC_RESVSP64
This command is used to allocate space to a file. A range of bytes is specified using a pointer
to a variable of type xfs_flock64_t in the final argument. The blocks are allocated, but not
zeroed, and the file size does not change. If the XFS filesystem is configured to flag unwritten
file extents, performance will be negatively affected when writing to preallocated space, since
extra filesystem transactions are required to convert extent flags on the range of the file
written. If xfs_info(8) reports unwritten=1, then the filesystem was made to flag unwritten
extents.

XFS_IOC_UNRESVSP
XFS_IOC_UNRESVSP64
This command is used to free space from a file. A range of bytes is specified using a pointer to
a variable of type xfs_flock64_t in the final argument. Partial filesystem blocks are zeroed, and
whole filesystem blocks are removed from the file. The file size does not change.

XFS_IOC_ZERO_RANGE
This command is used to convert a range of a file to zeros without issuing data IO. A range of
bytes is specified using a pointer to a variable of type xfs_flock64_t in the final argument.
Blocks are preallocated for regions that span holes in the file, and the entire range is converted
to unwritten extents. This operation is a fast method of overwriting any from the range specified
with zeros without removing any blocks or having to write zeros to disk. Any subsequent read in
the given range will return zeros until new data is written. This functionality requires
filesystems to support unwritten extents. If xfs_info(8) reports unwritten=1, then the filesystem
was made to flag unwritten extents.

XFS_IOC_PATH_TO_HANDLE
XFS_IOC_PATH_TO_FSHANDLE
XFS_IOC_FD_TO_HANDLE
XFS_IOC_OPEN_BY_HANDLE
XFS_IOC_READLINK_BY_HANDLE
XFS_IOC_ATTR_LIST_BY_HANDLE
XFS_IOC_ATTR_MULTI_BY_HANDLE
XFS_IOC_FSSETDM_BY_HANDLE
These are all interfaces that are used to implement various libhandle functions (see
open_by_handle(3)). They are all subject to change and should not be called directly by
applications.

Filesystem Operations
In order to effect one of the following operations, the pathname and descriptor arguments passed to
xfsctl() can be any open file in the XFS filesystem in question.

XFS_IOC_FSINUMBERS
See ioctl_xfs_fsinumbers(2) for more information.

XFS_IOC_FSGEOMETRY
See ioctl_xfs_fsop_geometry(2) for more information.

XFS_IOC_AG_GEOMETRY
See ioctl_xfs_ag_geometry(2) for more information.

XFS_IOC_FSBULKSTAT or XFS_IOC_FSBULKSTAT_SINGLE
See ioctl_xfs_fsbulkstat(2) for more information.

XFS_IOC_SCRUB_METADATA
See ioctl_xfs_scrub_metadata(2) for more information.

XFS_IOC_FSCOUNTS
See ioctl_xfs_fscounts(2) for more information.

XFS_IOC_GET_RESBLKS
XFS_IOC_SET_RESBLKS
See ioctl_xfs_getresblks(2) for more information. Save yourself a lot of frustration and avoid
these ioctls.

XFS_IOC_GOINGDOWN
See ioctl_xfs_goingdown(2) for more information.

XFS_IOC_THAW
XFS_IOC_FREEZE
XFS_IOC_FSGROWFSDATA
XFS_IOC_FSGROWFSLOG
XFS_IOC_FSGROWFSRT
These interfaces are used to implement various filesystem internal operations on XFS filesystems.
The remainder of these operations will not be described further as they are not of general use to
applications.

NAME

C SYNOPSIS

DESCRIPTION

SEE ALSO